6 th Grade Science Module 2 Physical vs Chemical Changes

hi iUniversity Prep today we're going to talk about physical versus chemical changes let's start with physical changes physical change is change that takes place that doesn't change the inherent properties of that substance it's still the same chemical for example we have some household aluminum foil if rip this foil in half it is still just aluminum foil if you zoomed in with microscope the atoms the molecules are still aluminum foil we have not changed that so that's just physical change if we change the size the shape the volume if crumpled this up have not changed the molecules of the foil it is still just aluminum foil whatever molecules make up aluminum foil which most of it's just aluminum it's still just that if bend it some more break it twist it turn it those are all just physical changes so let's talk about chemical changes what is chemical change chemical change is when you get new substance that cannot easily be undone for example if you baked cake if you took eggs flour sugar or whatever else you want to put in it and you heat it up and you bake cake you can't easily undo that you can't take that cake and turn it back into eggs flour and sugar that is new substance and there's lot of other chemical reactions out there and way to remember if chemical reaction has taken place is city guys love their cell phones let's start with the for city that stands for corrosion or rust take iron for example if you leave your bicycle out in the rain for year after while it will rust this orange red material forms that's new substance that's iron combining with oxygen in the air rearranging and you have new product new substance it is no longer just iron and just oxygen so that's chemical reaction stands for gas or bubbles so if you mix two chemicals together and you produce gas and bubbles you're pretty positive that chemical reaction has taken place now let's talk about love - if light is produced if light is produced by mixing two chemicals together you better believe it's chemical reaction in order for light to be produced that doesn't come from nowhere it has to come from somewhere electrons rearranging and releasing lot of energy to the point where light is produced so if you see light produced you know it's chemical reaction stands for temperature change if you mix two chemicals together and heat is produced or if it gets cold an endothermic reaction you better believe chemical reaction took place now the exception is if you take pot and put it on hot stove and the pot gets hot that's not chemical reaction because we didn't get new substance remember overall you have to have new substance for chemical reaction to take place all right so let's go to that next that stands for color change pick anything that has color the reason it has color is because that's the molecules reflecting that light so if you change the color of substance you are changing the molecule - precipitate so precipitate is little less common you don't really see that everyday so what is precipitate precipitate is when you mix two liquids together and you get solid and that doesn't happen often if you mix water and milk together it doesn't just magically form solid so we're gonna look at an example where mixing two liquids together makes solid alright so we talked about evidence of chemical change one of the main ones is precipitate forming when two liquids form solid so we have great example of that and another evidence happens see if you can catch that so right here we have sodium hydroxide solution and we have lead nitrate solution now don't blink here we go so two chemical reaction evidences just took place we have color change and precipitate now remember said two liquids making solid and if go in here we actually have little solid chunks now we went from two liquids to solid and definitely color change as you can see